[Intel-gfx] [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object

[Ben Widawsky]

Context save and restore is by definition a slow process, however it is
also an infrequent process. Don't try to optimize the save restore at
the cost of any of our precious cache space. Contexts begin to get quite
large on HSW and beyond.

At least for benchmarks people seem to care about, there is almost
always only 1 context running, which means I don't expect this to do any
harm. For benchmarks with many contexts, there could be performance
degradation - but I have a sneaking suspicion the HW will do some fancy
magic to speak up context save & restores anyway.

CC: Chris Wilson <chris at chris-wilson.co.uk>
CC: Eero Tamminen <eero.t.tamminen at intel.com>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 26c3fcc..593be55 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -153,13 +153,10 @@ create_hw_context(struct drm_device *dev,
 		return ERR_PTR(-ENOMEM);
 	}
 
-	if (INTEL_INFO(dev)->gen >= 7) {
-		ret = i915_gem_object_set_cache_level(ctx->obj,
-						      I915_CACHE_L3_LLC);
-		/* Failure shouldn't ever happen this early */
-		if (WARN_ON(ret))
-			goto err_out;
-	}
+	ret = i915_gem_object_set_cache_level(ctx->obj, I915_CACHE_NONE);
+	/* Failure shouldn't ever happen this early */
+	if (WARN_ON(ret))
+		goto err_out;
 
 	/* The ring associated with the context object is handled by the normal
 	 * object tracking code. We give an initial ring value simple to pass an
-- 
1.8.4